Method for forming a flip chip pressure sensor die package

ABSTRACT

A plurality of pressure sensor dice are attached to an array of pressure sensor die attach sites located on a custom substrate having holes. The pressure sensor dice are then electrically connected to the pressure sensor die attach sites using standard flip chip techniques. 
     The resulting array of pressure sensor sub-assemblies is then molded, so that a cavity is formed that is open at the bottom of each hole in the custom substrate. A portion of the outer surface of the micro-machine element of each pressure sensor die is left exposed at the bottom of the hole in the substrate. After molding, the exposed outer surface of the micro-machine element is covered with a pressure coupling gel applied in the hole. The resulting array of packaged pressure sensors are then sigulated using well know sawing or laser techniques or by snapping a specially formed snap array.

FIELD OF THE INVENTION

The present invention relates generally to the packaging of electroniccomponents. More particularly, the present invention relates to flipchip pressure sensor die packages.

BACKGROUND OF THE INVENTION

FIG. 1A illustrates a pressure sensor die 10 suitable for use with thepresent invention. In one embodiment, pressure sensor die 10 is apiezoresistive pressure sensor. Piezoresistive pressure sensors arediscussed, and one method for making piezoresistive pressure sensors isdisclosed, in U.S. Pat. No. 5,719,069, entitled “ONE-CHIP INTEGRATEDSENSOR PROCESS”, issued Feb. 17, 1998 to Sparks, which is incorporated,in its entirety, by reference herein. Another type of pressure sensor isdisclosed in U. S. Pat. 3,748,571, entitled “PRESSURE SENSITIVETRANSDUCERS EMPLOYING CAPACITIVE AND RESISTIVE VARIATIONS”, issued Jul.24, 1973 to Kurtz, which is also incorporated, in its entirety, byreference herein.

Pressure sensors and pressure sensor die assemblies are well known tothose of skill in the art and come in a large variety of sizes andconfigurations. Consequently, while one embodiment of a pressure sensordie 10 is discussed below, it will be recognized by those of skill inthe art that numerous other types of pressure sensors will work equallywell with the present invention.

Referring back to FIG. 1A, pressure sensor die 10 includes a pressuresensitive micro-machine element 54 which is a pressure sensing membranecomposed of a portion of the epitaxial silicon layer 16. Pressure sensordie 10 also includes a plurality of piezoresistors 14 formed inepitaxial silicon layer 16. Piezoresistors 14 serve as sensing elementsfor micromachine element 54.

Pressure sensor die 10 is formed by bonding a substrate 18 to a glass orsilicon wafer 20. Substrate 18 includes a cavity 22 such that whensubstrate 18 is bonded to wafer 20, wafer 20 seals cavity 22. Cavity 22is positioned directly below micro-machine element 54. In oneembodiment, wafer 20 hermetically seals cavity 22 so that pressuresensor die 10 is an absolute pressure sensor.

FIG. 1B shows another embodiment of a pressure sensor die 10B, whichincludes a die hole 60 through wafer 20 to vent cavity 22 makingpressure sensor die 10B a differential pressure sensor. As discussed inmore detail below, the method and structure of the present inventionworks equally well with both absolute pressure sensors, such as pressuresensor die 10, and differential pressure sensors, such as pressuresensor die 10B.

Pressure sensor die 10 or 10B is typically used to monitor the pressureof an external fluid, i.e., a gas or liquid, by placing first or outersurface 56 of pressure sensor die 10 or pressure sensor die 10B,including micro-machine element 54, in contact with the external fluid.During normal operation of pressure sensor die 10 or 10B, micro-machineelement 54 flexes in response to pressure on first or outer surface 56.This flex is sensed by piezoresistors 14 and processed to determine thepressure exerted on first or outer surface 56 by the external fluid,i.e., the pressure of the liquid or gas.

The structure and operation of pressure sensors, such as pressure sensordie 10 and pressure sensor die 10B, is well known to those of skill inthe art. Consequently, a more detailed discussion of the structure andoperation of pressure sensor die 10 and pressure sensor die 10B isomitted here to avoid detracting from the present invention. However, itis worth noting here that, as discussed above, in order for pressuresensor die 10 or pressure sensor die 10B to function, first or outersurface 56, including micro-machine element 54 must be flexibly coupledto the surrounding environment and cannot be shielded from thatenvironment by interposing layers of packaging material such as plasticsor epoxies.

FIG. 1C is an enlarged cross-sectional view of a pressure sensorsub-assembly 100 including a pressure sensor die 110 mounted on asubstrate 102 in die attach region 131. Like pressure sensor die 10 ofFIG. 1A, pressure sensor die 110 (FIG. 1C) includes a pressure sensitivemicro-machine element 154 composed of a portion of the epitaxial siliconlayer 116. Like pressure sensor die 10 discussed above, pressure sensordie 110 is formed by bonding a substrate 118 to a glass or silicon wafer120. Substrate 118 includes a cavity 122 such that when substrate 118 isbonded to wafer 120, wafer 120 seals cavity 122. Cavity 122 ispositioned directly below micro-machine element 154.

Pressure sensor die 110 is attached to a first surface 111 (a die attachsurface) of substrate 102 in die attach region 131 using any one ofseveral well-known adhesives 104. Substrate 102 is typically a printedcircuit board (PCB). In one embodiment, electrically conductive contactsor pads 106 on first or outer surface 130 of pressure sensor die 110 areconnected with electrically conductive bond wires 103 to electricallyconductive traces 112 and/or electrically conductive regions (not shown)formed on first surface 111 of substrate 102. Electrically conductivevias 114 are formed through substrate 102, from traces 112 and/orregions on first surface 111 to a second surface (the mounting surface)140 of substrate 102 which is opposite first surface 111. Electricallyconductive traces 113 formed on second surface 140 of substrate 102extend to electrically conductive contact or pads 115 formed on secondsurface 140 of substrate 102. Electrically conductive contacts 115 areused to connect substrate 102 and pressure sensor die 110 to a largersystem, such as a mother board (not shown), using well known methodssuch as solder balls, pins, leadless carrier chip (LCC) contacts orother surface mounts.

SUMMARY OF THE INVENTION

In accordance with the present invention, a plurality of pressure sensordie packages are fabricated simultaneously, in an array, to minimize thecost associated with each individual pressure sensor die package.

In one embodiment of the invention, a plurality of pressure sensor diceare attached to an array of pressure sensor die sites located on asubstrate. The pressure sensor dice are then electrically connected tothe pressure sensor die sites using, in one embodiment, standard wirebond techniques.

The resulting array of pressure sensor die sub-assemblies is thenmolded, in one embodiment of the invention, using a mold tool thatcloses on three sides of the substrate so that a cavity is formed thatis open on the fourth side. To this end, a first portion of the moldingtool has a plurality of insert pins that close on the outer surface ofeach pressure sensor die.

As a result, using the method of the invention, a portion of the outersurface of the micro-machine element of each pressure sensor die is leftexposed at the bottom of a cavity in the molding encapsulant. Aftermolding, the exposed outer surface of the micro-machine element iscovered with a pressure coupling gel that is applied in the shallowcavity. The coupling gel protects micro-machine elements from theenvironment, yet is compressible and is capable of coupling pressurefrom the external environment to the micro-machine elements.

The resulting array of packaged pressure sensor dice are then sigulatedusing well known sawing or laser techniques or by snapping a speciallyformed snap array.

In another embodiment of the invention, a hole is formed in the arraysubstrate and the pressure sensor substrate to accommodate adifferential pressure sensor die.

In another embodiment of the invention, a custom substrate is formedwith a plurality of holes formed, one each, at pressure sensor diemounting sites. A plurality of pressure sensor dice are then attached topressure sensor die mounting sites located on the substrate. Thepressure sensor dice are then electrically connected to the pressuresensor sites using, in this embodiment, standard flip-chip techniques.

The resulting array of pressure sensor die sub-assemblies is thenmolded, using a mold tool that closes on the substrate and is filledwith encapsulant.

Using this embodiment of the method of the invention, a portion of theouter surface of the micro-machine element of each pressure sensor dieis left exposed at the bottom of the holes in the substrate. Aftermolding, the exposed outer surface of the micro-machine element iscovered with a pressure coupling gel applied in the hole in thesubstrate. The resulting array of packaged pressure sensors are thensigulated using well known sawing or laser techniques or by snapping aspecially formed snap array.

In another embodiment of the invention, a cavity is formed in theencapsulant and the pressure sensor substrate to accommodate adifferential pressure sensor die.

In particular, one embodiment of the method of the invention includes:providing a pressure sensor die, the pressure sensor die having apressure sensor die first surface and a pressure sensor die secondsurface, opposite the pressure sensor die first surface; providing asubstrate, the substrate having a substrate first surface and asubstrate second surface, opposite the substrate first surface, thesubstrate first surface having a die attach region, the substrate havinga hole connecting the substrate first surface and the substrate secondsurface, the hole being located in the die attach region of thesubstrate first surface; attaching the pressure sensor die first surfaceto the substrate first surface in the die attach region such that afirst region of the pressure sensor die first surface covers the hole inthe die attach region; and applying encapsulant to at least a portion ofthe substrate first surface and the pressure sensor die second surface,the encapsulant having an outer surface.

One embodiment of the method of the present invention also includesfilling at least a portion of the hole in the substrate with couplinggel such that the coupling gel covers the first region of the pressuresensor die first surface.

These and other features and advantages of the present invention will bemore readily apparent from the detailed description set forth belowtaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an absolute pressure sensor die suitable for usewith the present invention;

FIG. 1B illustrates a differential pressure sensor die suitable for usewith the present invention;

FIG. 1C an enlarged cross-sectional view of a pressure sensor diemounted on a substrate prior to packaging using prior art methods;

FIG. 2A shows an enlarged cross-sectional view of one embodiment of anabsolute sensor die package in accordance with the invention;

FIG. 2B shows an enlarged cross-sectional view of a differential asensor die package according to another embodiment of the invention;

FIG. 3A shows a multi-package array sub-assembly according to theprinciples of the invention;

FIG. 3B shows a lower mold section of a mold used to fabricate pressuresensor die packages according to one embodiment of the invention;

FIG. 3C shows the multi-package array sub-assembly of FIG. 3A positioneda cavity of the lower mold section of FIG. 3B on a cavity bottom surfaceaccording to the principles of the invention;

FIG. 3D shows the multi-package array sub-assembly of FIG. 3A positionedin the cavity of the lower mold section on the cavity bottom surfacewith an upper mold section positioned above the lower mold sectionaccording to the principles of the invention;

FIG. 3E shows the upper mold section positioned on the lower moldsection just prior to introduction of encapsulant according to theprinciples of the invention;

FIG. 3F shows the upper mold section positioned on the lower moldsection, as in FIG. 3E, with encapsulant being introduced to thestructure according to the principles of the invention;

FIG. 3G shows the upper mold section positioned on the lower moldsection, as in FIG. 3F, with encapsulant having been introduced andflowed throughout the structure according to the principles of theinvention.

FIG. 3H shows the upper mold section removed from the lower mold sectionafter molding according to the principles of the invention;

FIG. 3I shows the multi-package array sub-assembly removed from thelower mold section after molding according to the principles of theinvention;

FIG. 3J shows the multi-package array sub-assembly of FIG. 3I with acoupling gel applied to, and filling, a portion of the cavities formedaccording to the of cavities formed according to the principles of theinvention;

FIG. 3K shows the multi-package array sub-assembly of FIG. 3J withsolder balls attached, thereby forming a ball grid array pressure sensordie array according to the principles of the invention;

FIG. 3L shows a ball grid array pressure sensor die package of FIG. 3Kafter singulation from the multi-package array sub-assembly according tothe principles of the invention;

FIG. 4A shows an enlarged cross-sectional view of a flip-chip absolutepressure sensor die package in accordance with the principles of theinvention;

FIG. 4B shows an enlarged cross-sectional view of a flip-chipdifferential pressure sensor die package according to the principles ofanother embodiment of the invention;

FIG. 5A shows a multi-package array substrate customized according tothe principles of the invention to include holes;

FIG. 5B shows a multi-package array sub-assembly according to theprinciples of the invention;

FIG. 5C shows a lower mold section of a mold used to fabricate flip-chippressure sensor die packages according to the principles of oneembodiment of the invention;

FIG. 5D shows the multi-package array sub-assembly of FIG. 5B positionedin a cavity of the lower mold section on the cavity bottom surfaceaccording to the principles of the invention;

FIG. 5E shows the multi-package array sub-assembly of FIG. 5B positionedin the cavity of the lower mold section on the cavity bottom surfacewith an upper mold section positioned above the lower mold sectionaccording to the principles of the invention;

FIG. 5F shows the upper mold section positioned on the lower moldsection just prior to introduction of encapsulant according to theprinciples of the invention;

FIG. 5G shows the upper mold section positioned on the lower moldsection, as in FIG. 5F, with encapsulant being introduced to thestructure according to the principles of the invention;

FIG. 5H shows the upper mold section positioned on the lower moldsection, as in FIG. 5G, with encapsulant having been introduced andflowed throughout the structure according to the principles of theinvention;

FIG. 5I shows the upper mold section removed from the lower mold sectionafter molding according to the principles of the invention;

FIG. 5J shows the multi-package array sub-assembly removed from thelower mold section after molding according to the principles of theinvention;

FIG. 5K shows the multi-package array sub-assembly of FIG. 5J with acoupling gel applied to, and filling a portion of, the holes accordingto the principles of the invention;

FIG. 5L shows the multi-package array sub-assembly of FIG. 5K withsolder balls attached, thereby forming a flip-chip ball grid arraypressure sensor die package array according to the principles of theinvention; and

FIG. 5M shows ball grid array pressure sensor die package of FIG. 5Lafter singulation from multi-package array sub-assembly according to theprinciples of the invention.

In the following description, similar elements are labeled with similarreference numbers.

DETAILED DESCRIPTION

In accordance with the present invention, a plurality of pressure sensordie packages (FIGS. 2A, 2B, 3L, 4A, 4B and 5M) are fabricatedsimultaneously in an array (FIGS. 3K and 5L) to minimize the costassociated with each individual pressure sensor die package (FIGS. 2A,2B, 3L, 4A, 4B and 5M).

In one embodiment of the invention, a plurality of pressure sensor dice(310A, 310B and 310C in FIG. 3A) are attached to an array of pressuresensor sites located on a substrate (FIG. 3A). The pressure sensor diceare then electrically connected to the pressure sensor die attach sitesusing, in one embodiment, standard wire bond techniques (FIG. 3A).

In one embodiment of the invention, the resulting array of pressuresensor die sub-assemblies (300 in FIG. 3A) is then molded, using a moldtool (370 and 376 in FIGS. 3B to 3I) that closes on three sides of thesubstrate so that a cavity (362A, 362B and 362C in FIG. 3I) is formedthat is open on the fourth side. A first portion of the molding tool(376 in FIGS. 3F to 3I) has a plurality of insert pins (378A, 378B and378C in FIG. 3F) that close on the outer surface of each pressure sensordie (310A, 310B and 310C In FIG. 3F).

Using the method of the invention, a portion of the outer surface (354A,354B, and 354C in FIG. 3I) of the micro-machine element of each pressuresensor die (310A, 310B and 310C in FIG. 3I) is left exposed at thebottom of a cavity (362A, 362B and 362C in FIG. 3I) in the moldingencapsulant (364 in FIG. 3I). After molding, the exposed outer surfaceof the micro-machine element (354A, 354B, and 354C in FIG. 3I) iscovered with a pressure coupling gel (360A, 360B and 360C in FIG. 3J)applied in the cavity (362A, 362B and 362C in FIG. 3J). Coupling gel360A, 360B and 360C protects micro-machine elements 354A, 354B and 354C,respectively, from the environment, yet is compressible and is capableof coupling pressure from the external environment to micro-machineelements 354A, 354B and 354C, respectively.

The resulting array of packaged pressure sensors (300A, 300B, and 300Cin FIG. 3K) are then sigulated using well know sawing or lasertechniques or by snapping a specially formed snap array.

In another embodiment of the invention, a hole (290 in FIG. 2B) isformed in the array substrate (202 in FIG. 2B) and the pressure sensorsubstrate (220 in FIG. 2B) to accommodate a differential pressure sensordie (210B in FIG. 2B).

In another embodiment of the invention, a custom substrate (502 In FIG.5A) is formed with a plurality of holes (462, 560, 561, 562A, 562B, and562C in FIG. 5A) formed, one each, at pressure sensor die mounting sites(402, 502A, 502B, 502C, 502D and 502E in FIG. 5A). A plurality ofpressure sensor dice (510A, 510B and 510C in FIG. 5B) is then attachedto pressure sensor die mounting sites located on the substrate (FIG.5B). The pressure sensor dice are then electrically connected to thepressure sensor sites using, in this embodiment, standard flip-chiptechniques (FIG. 5B).

The resulting array of pressure sensor die sub-assemblies (511A, 511Band 511C in FIG. 5B) is then molded, using a mold tool (570 and 576 inFIGS. 5C to 5I) that closes on the substrate and is filled withencapsulant (FIGS. 5C to 5I).

Using this embodiment of the method of the invention, a portion of theouter surface (554A, 554B, and 554C in FIG. 5J) of the micro-machineelement of each pressure sensor die (510A, 5l0B and 510C in FIG. 5J) isleft exposed at the bottom of the holes (562A, 562B and 562C in FIG. 5J)in the substrate (502 in FIG. 5J). After molding, the exposed outersurface of the micro-machine element (554A, 554B, and 554C in FIG. 5J)is covered with a pressure coupling gel (560A, 560B and 560C in FIG. 5K)applied in the holes (562A, 562B and 562C in FIG. 5K). The resultingarray of packaged pressure sensors (500A, 500B, and 500C in FIG. 5L) arethen sigulated using well know sawing or laser techniques or by snappinga specially formed snap array.

In another embodiment of the invention, a second hole (490 in FIG. 4B)is formed in the encapsulant (464 in FIG. 4B) and the pressure sensorsubstrate (420 in FIG. 4B) to accommodate a differential pressure sensordie (410B in FIG. 4B).

FIG. 2A shows an enlarged cross-sectional view of one embodiment of apressure sensor die package 200A in accordance with the invention.Pressure sensor die package 200A includes a pressure sensor die 210mounted on a substrate 202 in a die attach region 231. Like pressuresensor die 10 of FIG. 1A, pressure sensor die 210 (FIG. 2A) includes apressure sensitive micro-machine element 254 composed of a portion ofthe epitaxial silicon layer 216. Like pressure sensor die 10 discussedabove, pressure sensor die 210 is formed by bonding a substrate 218 to aglass or silicon wafer 220. Substrate 218 includes a cavity 222 suchthat when substrate 218 is bonded to wafer 220, wafer 220 seals cavity222. Cavity 222 is positioned directly below micro-machine element 254.

Pressure sensor die 210 is attached to a first surface 211 (a die attachsurface) of substrate 202 in die attach region 231 using any one ofseveral well-known adhesives 204. Substrate 202 is typically a printedcircuit board (PCB). In one embodiment, electrically conductive pads 206on first surface 230 of pressure sensor die 210 are connected withelectrically conductive bond wires 203 to electrically conductive traces212 and/or electrically conductive regions (not shown) formed on firstsurface 211 of substrate 202. In one embodiment of the invention,electrically conductive vias 214 are formed by methods well know tothose of skill in the art. Electrically conductive vias 214 are formedthrough substrate 202, from traces 212 and/or regions on first surface211 to a second surface (the mounting surface) 240 of substrate 202which is opposite first surface 211. Electrically conductive traces 212formed on second surface 240 of substrate 202 extend to electricallyconductive contacts or pads 215 formed on second surface 240 ofsubstrate 202. Electrically conductive pads 215 are used to connectsubstrate 202 and pressure sensor die 210 to a larger system, such as amother board (not shown), using well known methods such as solder balls,pins, leadless carrier chip (LCC) contacts or other surface mounts.

According to the invention, pressure sensor die package 200A alsoincludes encapsulant 264 that forms, as discussed in more detail below,cavity 262 with sides 266 and 267. In one embodiment of the invention,cavity 262 has length parallel to micro-machine element 254 ofapproximately 0.5 mm to 1.0 mm (19.7 mils to 39.4 mils) and a depthperpendicular to micro-machine element 254 that varies from applicationto application from 25 to 100 microns. Cavity 262 is positioned directlyover micro-machine element 254. A bottom portion 263 of cavity 262 is,according to the invention, filled with coupling gel 260. Coupling gel260 is, in one embodiment, typically a silicon gel such as thoseproduced by Dow Corning and well known to those of skill in the art.

FIG. 2B shows an enlarged cross-sectional view of a pressure sensor diepackage 200B according to another embodiment of the invention. In FIG.2B, pressure sensor die 210B is a differential pressure sensor die. Theoperation of differential pressure sensors and differential pressuresensor dice, such as pressure sensor die 210B, is well known to those ofskill in the art. Therefore, the operation of differential sensor die210B will not be discussed in detail herein to avoid detracting from theinvention.

Pressure sensor die package 200B is identical to pressure sensor diepackage 200A, discussed above with respect to FIG. 2A, except thatpressure sensor die package 200B includes a die hole 290 through wafer220 to cavity 222 of sensor die 210 and a substrate through hole 292through substrate 202 which is at least partially aligned with die hole290. Hole 290 die hole 290 and substrate through hole 292 allow pressuresensor die 210 to act as a differential pressure sensor.

In accordance with the present invention, a plurality of pressure sensordie packages, such as pressure sensor die package 200A (FIG. 2A) orpressure sensor die package 200B (FIG. 2B), are fabricatedsimultaneously to minimize the cost associated with each individual diepackage. FIGS. 3A to 3L show the significant steps involved in makingone embodiment of a pressure sensor die package according to theinvention. In FIGS. 3A to 3L, a method for making an absolute pressuresensor die package, such as pressure sensor die package 200A in FIG. 2A,is shown in detail. However, those of skill in the art will recognizethat by using a custom substrate, such as substrate 502 in FIG. 5A(discussed below), or by cutting through hole 292 in a standardsubstrate, such as substrate 202 in FIG. 3A, the method of the inventioncan be used to fabricate a differential pressure sensor package, such asdifferential pressure sensor package 200B in FIG. 2B. A method formaking an absolute pressure sensor package is discussed in detail below,and shown in FIGS. 3A to 3L, for simplicity sake only and to keep thepresent discussion as brief and simple as possible. Consequently, thechoice of this one embodiment of the invention for the dicussion belowis not meant to limit the scope of the present invention to thisembodiment.

FIG. 3A shows a multi-package array sub-assembly 300. Multi-packagearray sub-assembly 300 includes substrate 302 made up of individualpackage substrate sections 302A, 302B and 302C. Individual packagesubstrate sections 302A, 302B and 302C are identical to substrate 202 ofFIG. 2A discussed above. As shown in FIG. 3A, each individual packagesubstrate section 302A, 302B and 302C has a pressure sensor die 310A,310B and 310C, respectively, mounted on a first surface 311A, 311B and311C, respectively.

FIG. 3B shows a lower mold section 370 of a custom mold used tofabricate pressure sensor die packages according to one embodiment ofthe invention. Lower mold section 370 includes cavity 374 with cavitybottom surface 372.

FIG. 3C shows multi-package array sub-assembly 300 positioned in cavity374 of lower mold section 370 on cavity bottom surface 372.

FIG. 3D shows multi-package array sub-assembly 300 positioned in cavity374 of lower mold section 370 on cavity bottom surface 372 with uppermold section 376 positioned above lower mold section 370. Upper moldsection 376 includes pins 378A, 378B and 378C that extend from surface379 of upper mold section 376.

FIG. 3E shows upper mold section 376 positioned on lower mold section370 just prior to introduction of encapsulant. AS shown in FIG. 3E, whenupper mold section 376 is in place, pins 378A, 378B and 378C of uppermold section 376 make physical contact with micro-machine elements 354A,354B and 354C, respectively, of pressure sensor dice 310A, 310B and310C, respectively. In addition, when upper mold section 376 is in placeon lower mold section 370, a channel 375 is formed for the introductionof liquid encapsulant.

FIG. 3F shows upper mold section 376 positioned on lower mold section370, as in FIG. 3E, with encapsulant 364 being introduced to thestructure.

FIG. 3G shows upper mold section 376 positioned on lower mold section370, as in FIG. 3F, with encapsulant 364 having been introduced andflowed throughout the structure. As can be seen in FIG. 3G, encapsulant364 covers the entire first surfaces 311A, 311B and 311C of individualpackage substrate sections 302A, 302B, 302C, respectively, as well asthe majority of pressure sensors 310A, 310B and 310C. Importantly,however, encapsulant 364 is prevented for covering a first region of thefirst surfaces of pressure sensors 310A, 310B and 310C includingmicro-machine elements 354A, 354B and 354C by pins 378A, 378B and 378C,respectively.

FIG. 3H shows upper mold section 376 removed from lower section 370after molding, As can be seen in FIG. 3H, after molding according to theinvention, cavities 362A, 362B and 362C are formed in encapsulant 364such that a first region of the first surfaces of pressure sensors 310A,310B and 310C including micro-machine elements 354A, 354B and 354Cremain exposed at the bottom of cavities 362A, 362B and 362C,respectively.

FIG. 3I shows multi-package array sub-assembly 300 removed from lowermold section 370 (FIG. 3G) after molding. As seen in FIG. 3I, aftermolding, each pressure sensor die 310A, 310B and 310C has a first regionof the first surfaces of pressure sensors 310A, 310B and 310C includingmicro-machine element 354A, 354B and 354C, respectively, exposed to theenvironment at the bottom of cavities 362A, 362B and 362C, respectively.

FIG. 3J shows multi-package array sub-assembly 300 of FIG. 3I with acoupling gel 360A, 360B and 360C applied to, and filling a portion of,cavities 362A, 362B and 362C, respectively. Coupling gel 360A, 360B and360C protects micro-machine elements 354A, 354B and 354C, respectively,from the environment, yet is compressible and is capable of couplingpressure from the external environment to micro-machine elements 354A,354B and 354C, respectively.

FIG. 3K shows multi-package array sub-assembly 300 of FIG. 3J withsolder balls 390 attached, thereby forming ball grid array pressuresensor die package array 399 including ball grid array pressure sensorpackages 300A, 300B and 300C.

FIG. 3L shows ball grid array pressure sensor package 300B of FIG. 3Kafter singulation from multi-package array sub-assembly 300.

Singulation of ball grid array pressure sensor die package 300B isachieved by any singulation method such as sawing, laser or snappingmethods.

FIG. 4A shows an enlarged cross-sectional view of another embodiment ofa pressure sensor die package 400A in accordance with the invention.Pressure sensor die package 400A includes a pressure sensor die 410mounted on a substrate 402. Like pressure sensor die of FIG. 1A,pressure sensor die 410 (FIG. 4A) includes a pressure sensitivemicro-machine element 454 composed of a portion of the epitaxial siliconlayer 416. Like pressure sensor die 10 discussed above, pressure sensordie 410 is formed by bonding a substrate 418 to a glass or silicon wafer420. Substrate 418 includes a cavity 422 such that when substrate 418 isbonded to wafer 420, wafer 420 seals cavity 422. Cavity 422 ispositioned directly below micro-machine element 454.

In the embodiment of the invention shown in FIG. 4A, pressure sensor die410 is attached to a first surface 411 (a die attach surface) ofsubstrate 402 in a “flip-chip” configuration. Flip-chip configurationsare well known to those of skill in the art and are therefore notdiscussed in detail here to avoid detracting from the invention. Oncepressure sensor die 410 is attached to first surface 411 of substrate402 in die attach region 431 in the flip-chip configuration, an underfill material 404 is applied between first surface 411 and pressuresensor die 410. Under filling and under fill materials are well known tothose of skill in the art.

Substrate 402 is typically a printed circuit board (PCB) that, asdiscussed in more detail below, is customized according to the inventionfor flip-chip applications of pressure sensor die 410. In particular,substrate 402 includes pre-cut hole 462 with sides 466 and 467. Asdiscussed in more detail below, in one embodiment of the invention, hole462 has a length of 1.0 mm (39.4 mils) and a width of 1.0 mm (39.4mils). Hole 462 is positioned directly over micro-machine element 454and a first region of a first surface 430 of pressure sensor die 410. Inaddition, a bottom portion 463 of hole 462 is, according to theinvention, filled with coupling gel 460. Coupling gel 460 protectsmicro-machine element 454 from the environment, yet is compressible andis capable of coupling pressure from the external environment tomicro-machine element 454. Coupling gel 460 is, in one embodiment,typically a silicon gel such as those produced by Dow Corning and wellknown to those of skill in the art.

In this embodiment of the invention, electrically conductive pads 406first surface 430 of pressure sensor die 410 are connected directly toelectrically conductive traces 412 and/or electrically conductiveregions (not shown) formed on first surface 411 of substrate 402. In oneembodiment of the invention, electrically conductive vias 414 are formedthrough substrate 402, from traces 412 and/or regions on first surface411 to a second surface (the mounting surface) 440 of substrate 402which is opposite first surface 411.

Electrically conductive traces 413 formed on second surface 440 ofsubstrate 402 extend to electrically conductive contacts or pads 415formed on second surface 440 of substrate 402. Electrically conductivepads 415 are used to connect substrate 402 and pressure sensor die 410to a larger system, such as a mother board (not shown), using well knownmethods such as solder balls, pins, leadless carrier chip (LCC) contactsor other surface mounts.

According to the invention, pressure sensor die package 400A alsoincludes encapsulant 464 that protects pressure sensor die 410 and firstsurface 411 of substrate 402 from the elements.

FIG. 4B shows an enlarged cross-sectional view of a pressure sensor diepackage 400B according to another embodiment of the invention. In FIG.4B, pressure sensor die 410B is a differential pressure sensor die. Theoperation of differential pressure sensors and differential pressuresensor dice, such as pressure sensor die 410B, is well known to those ofskill in the art. Therefore, the operation of differential sensor die410B will not be discussed in detail herein to avoid detracting from theinvention.

Pressure sensor die package 400B is identical to pressure sensor diepackage 400A, discussed above with respect to FIG. 4A, except thatpressure sensor die package 400B includes a die hole 490 through wafer420 to cavity 422 of sensor die 410 and encapsulant through hole 492through encapsulant 464 which is at least partially aligned with diehole 490. Through hole 490 allows pressure sensor die 410 to act as adifferential pressure sensor package.

In accordance with the present invention, a plurality of pressure sensordie packages, such as pressure sensor die package 400A (FIG. 4A) andpressure sensor die package 400B (FIG. 4B), are fabricatedsimultaneously to minimize the cost associated with each individualpackage. FIGS. 5A to 5M show the significant steps involved for makingone embodiment of a pressure sensor package according to the invention.In FIGS. 5A to 3M, a method for making an absolute pressure sensor diepackage, such as pressure sensor die package 400A in FIG. 4A, isdiscussed in detail. However, those of skill in the art will recognizethat by using a custom mold, such as mold 370 and 376 in FIG. 3E(discussed above), or by forming cutting an encapsulation through hole492 in encapsulant 464 in FIG. 4B, the method of the invention can beused to fabricate a differential pressure sensor die package, such asdifferential pressure sensor die package 400B in FIG. 4B. A method formaking an absolute pressure sensor package is discussed in detail below,and shown in FIGS. 5A to 5M, for simplicity sake only and to keep thepresent discussion as brief and simple as possible. Consequently, thechoice of this one embodiment of the invention for the discussion belowis not meant to limit the scope of the present invention to thisembodiment.

FIG. 5A shows a multi-package array substrate 502 customized accordingto the invention to include substrate holes 462, 560, 561, 562A, 562Band 562C. In one embodiment of the invention, multi-package arraysubstrate 502 is a PCB and includes substrate 402 of FIG. 4A with hole462 having sides 467 and 466. In addition, multi-package array substrate502 includes substrates 502A, 502B, 502C, 502D and 502E that arediscussed in more detail below.

Holes 462, 560, 561, 562A, 562B and 562C are formed by methods well knowto those of skill in the art such as punching the holes bore firing. Inone embodiment of the invention, holes 462, 560, 561, 562A, 562B and562C have a length 593 of 1.0 mm (39.4 mils) and a width 595 of 1.0 mm(39.4 mils).

Typically, multi-package array substrate 502 includes a nine by nine(9×9) array of substrates such as substrates 402, 502A, 502B, 502C, 502Dand 502E. However, multi-package array substrate 502 can include anynumber of substrates such as substrates 402, 502A, 502B, 502C, 502D and502E. Only six such substrates are shown in FIG. 5A for simplicity sake.

FIG. 5B shows a multi-package array sub-assembly 500. Multi-packagearray sub-assembly 500 includes multi-package array substrate 502, asseen along line 5B—5B of FIG. 5A, made up of individual packagesubstrates 502A, 502B and 502C. Individual package substrates 502A, 502Band 502C are identical to substrate 402 of FIG. 4A discussed above. Asshown in FIG. 5B, each individual package substrate 502A, 502B and 502Chas a pressure sensor die 510A, 510B and 510C, respectively, mounted ona first surface 511A, 511B and 511C, respectively, in a flip-chipconfiguration.

FIG. 5C shows a lower mold section 570 of a mold used to fabricatepressure sensor die packages according to one embodiment of theinvention. Lower mold section 570 includes cavity 574 with cavity bottomsurface 572.

FIG. 5D shows multi-package array sub-assembly 500 positioned in cavity574 of lower mold section 570 on cavity bottom surface 572.

FIG. 5E shows multi-package array sub-assembly 500 positioned in cavity574 of lower mold section 570 on cavity bottom surface 572 with uppermold section 576 positioned above lower mold section 570.

FIG. 5F shows upper mold section 576 positioned on lower mold section570 just prior to introduction of encapsulant. As shown in FIG. 5F, whenupper mold section 576 is in place on lower mold section 570, a channel575 is formed for the introduction of liquid encapsulant.

FIG. 5G shows upper mold section 576 positioned on lower mold section570, as in FIG. 5F, with encapsulant 564 being introduced to thestructure.

FIG. 5H shows upper mold section 576 positioned on lower mold section570, as in FIG. 5G, with encapsulant 564 having been introduced andflowed throughout the structure. As can be seen in FIG. 5H encapsulant564 covers the entire first surfaces 511A, 511B and 511C of individualpackage substrates 502A, 502B, 502C, respectively, as well as pressuresensor dice 510A, 510B and 510C.

FIG. 5I shows upper mold section 576 removed from lower section 570after molding. As can be seen in FIG. 5I, after molding according to theinvention, holes 562A, 562B and 562C of substrates 502A, 502B 502C arepositioned such that micro-machine elements 554A, 554B and 554C remainexposed at the bottom of holes 562A, 562B and 562C, respectively.

FIG. 5J shows multi-package array sub-assembly 500 removed from lowermold section 570 (FIG. 5H) after molding. As seen in FIG. 5J, aftermolding, each pressure sensor die 510A, 510B and 510C has itsmicro-machine element 554A, 554B and 554C, respectively, exposed to theenvironment at the bottom of holes 562A, 562B and 562C, respectively.

FIG. 5K shows multi-package array sub-assembly 500 of FIG. 5J with acoupling gel 560A, 560B and 560C applied to, and filling a portion, ofholes 562A, 562B and 562C, respectively. Coupling gel 560A, 560B and560C protects micro-machine elements 554A, 554B and 554C, respectively,from the environment, yet is compressible and is capable of couplingpressure from the external environment to micro-machine elements 554A,554B and 554C, respectively.

FIG. 5L shows multi-package array sub-assembly 500 of FIG. 5K withsolder balls 590 attached, thereby forming ball grid array pressuresensor die array 599 including ball grid array pressure sensor diepackages 500A, 500B and 500C.

FIG. 5M shows ball grid array pressure sensor die package 500B of FIG.5L after singulation from multi-package array sub-assembly 500.

Singulation of ball grid array pressure sensor die package 500B isachieved by any singulation method such as sawing, laser or snappingmethods.

This Application is related to: co-filed U.S. patent application Ser.No. 09/754,229, entitled “METHOD FOR FORMING A BOND WIRE PRESSURE SENSORPACKAGE”, and naming Steven Webster as inventor; co-filed U.S. patentapplication Ser. No. 09/754,393, entitled “BOND WIRE PRESSURE SENSORPACKAGE”, and naming Steven Webster as inventor; and co-filed U.S.patent application Ser. No. 09/754,487, entitled “FLIP CHIP PRESSURESENSOR PACKAGE”, and naming Steven Webster as inventor; all of which areassigned to the assignee of the present invention and are incorporatedherein, in their entirety, by reference for all purposes.

The drawings and the forgoing description gave examples of the presentinvention. The scope of the present invention, however, is by no meanslimited by these specific examples. Numerous variations, whetherexplicitly given in the specification or not, such as differences instructure, dimension, and use of material, are possible.

For instance, as discussed above, FIGS. 3A to 3L and FIGS. 5A to 5M,show a method for making an absolute pressure sensor die package.However, those of skill in the art will recognize that, by making minorvariations to the method shown, the method of the invention can be usedto fabricate a differential pressure sensor package. A method for makingan absolute pressure sensor package is discussed in detail above, andshown in FIGS. 3A to 3L and 5A to 5M, for simplicity sake only and tokeep the present discussion as brief and simple as possible. However,the scope of the invention is at least as broad as given by thefollowing claims.

What is claimed is:
 1. A method for making a pressure sensor die packagecomprising: providing a pressure sensor die, said pressure sensor diecomprising a pressure sensor die first surface and a pressure sensor diesecond surface, opposite said pressure sensor die first surface;providing a substrate, said substrate comprising a substrate firstsurface and a substrate second surface, opposite said substrate firstsurface, said substrate first surface comprising a die attach region,said substrate further comprising a hole connecting said substrate firstsurface and said substrate second surface, said hole being located insaid die attach region of said substrate first surface; attaching saidpressure sensor die first surface to said substrate first surface insaid die attach region such that a first region of said pressure sensordie first surface covers said hole in said die attach region; andapplying encapsulant to at least a portion of said substrate firstsurface and said pressure sensor die second surface, said encapsulantcomprising an outer surface.
 2. The method for making a pressure sensordie package of claim 1, further comprising: filling at least a portionof said hole in said substrate with coupling gel such that said couplinggel covers said first region of said pressure sensor die first surface.3. The method for making a pressure sensor die package of claim 2,wherein said hole in said substrate has a length and width parallel tosaid pressure sensor die first surface of approximately 1.0 mm square.4. The method for making a pressure sensor die package of claim 2,wherein said hole in said substrate is filled with coupling gel toapproximately at least 80% above said first region of said first surfaceof said pressure sensor die.
 5. The method for making a pressure sensordie package of claim 2 further comprising: forming solder bumps, saidsolder bumps electrically connecting electrical contacts on saidpressure sensor die first surface to electrical contacts on saidsubstrate first surface in a flip-chip configuration.
 6. The method formaking a pressure sensor die package of claim 5, wherein said pressuresensor die is an absolute pressure sensor die.
 7. The method for makinga pressure sensor die package of claim 6, further comprising: forming aplurality of solder balls on electrical contacts on said substratesecond surface.
 8. The method for making a pressure sensor die packageof claim 6, further comprising: forming a plurality pins on electricalcontacts on said substrate second surface.
 9. The method for making apressure sensor die package of claim 6, further comprising: forming aplurality leadless chip carrier contacts on electrical contacts on saidsubstrate second surface.
 10. The method for making a pressure sensordie package of claim 5, further comprising: forming an encapsulantthrough hole in said encapsulant, said encapsulant through holeextending from said outer surface of said encapsulant to a first regionof said second surface of said pressure sensor die.
 11. The method formaking a pressure sensor die package of claim 10, wherein said pressuresensor die is a differential pressure sensor die, said differentialpressure sensor die comprising a die hole connecting said second surfaceof said differential pressure sensor die to a cavity formed in saiddifferential pressure sensor die; and at least partially aligning saiddie hole with said encapsulant through hole.
 12. The method for making apressure sensor die package of claim 11, further comprising: forming aplurality of solder balls on electrical contacts on said substratesecond surface.
 13. The method for making a pressure sensor die packageof claim 11, further comprising: forming a plurality pins on electricalcontacts on said substrate second surface.
 14. The method for making apressure sensor die package of claim 11, further comprising: forming aplurality leadless chip carrier contacts on electrical contacts on saidsubstrate second surface.
 15. The method for making a pressure sensordie package of claim 11, wherein said pressure sensor die package has athickness measured from said substrate second surface to saidencapsulant outer surface of approximately 1.8 mm.
 16. The method formaking a pressure sensor die package of claim 2, wherein said pressuresensor die package has a thickness measured from said substrate secondsurface to said encapsulant outer surface of approximately 1.8 mm.
 17. Amethod for making pressure sensor die packages comprising: providing aplurality of pressure sensor dice, said pressure sensor dice eachcomprising a pressure sensor die first surface and a pressure sensor diesecond surface, opposite said pressure sensor die first surface; formingan array substrate, said array substrate comprising an array substratefirst surface and an array substrate second surface, opposite said arraysubstrate first surface, said array substrate first surface comprising aplurality of die attach regions, said array substrate comprising aplurality of holes connecting said array substrate first surface andsaid array substrate second surface, wherein; each die attach region ofsaid plurality of die attach regions has a corresponding one of saidplurality of holes therein; attaching each of said pressure sensor diefirst surfaces to said array substrate first surface in a correspondingone of said die attach regions such that a first region of each of saidpressure sensor die first surfaces covers said corresponding hole ineach of said die attach regions; and applying encapsulant to at least aportion of said array substrate first surface and said pressure sensordie second surfaces, said encapsulant comprising an outer surface. 18.The method for making pressure sensor die packages of claim 17, furthercomprising: filling at least a portion of each of said plurality ofholes in said array substrate with coupling gel such that each of saidfirst regions of said first surfaces of said plurality of pressuresensor dice is covered by said coupling gel.
 19. The method for makingpressure sensor die packages of claim 18, further comprising: formingsolder bumps, said solder bumps electrically connecting electricalcontacts on each of said plurality of pressure sensor dice firstsurfaces to electrical contacts on said array substrate first surface.20. The method for making pressure sensor die packages of claim 19,wherein each of said plurality of pressure sensor dice is an absolutepressure sensor die.
 21. The method for making pressure sensor diepackages of claim 19, further comprising: forming a plurality ofencapsulant through holes in said encapsulant, each encapsulant throughhole of said plurality of encapsulant through holes extending from saidencapsulant outer surface to a first region of said first surface ofeach of said plurality of pressure sensor dice.
 22. The method formaking pressure sensor die packages of claim 21, wherein each of saidplurality of pressure sensor dice is a differential pressure sensor die,said plurality of differential pressure sensor dice each comprising adie hole connecting said second surface of each of said differentialpressure sensor dice to a cavity formed in each of said differentialpressure sensor dice; and at least partially aligning each of said dieholes with one of said plurality of array substrate through holes.
 23. Amethod for making a pressure sensor die package comprising: providing apressure sensor die, said pressure sensor die comprising a pressuresensor die first surface and a pressure sensor die second surface,opposite said pressure sensor die first surface; providing a substrate,said substrate comprising a substrate first surface and a substratesecond surface, opposite said substrate first surface, said substratefirst surface comprising a die attach region, said substrate furthercomprising a hole connecting said substrate first surface and saidsubstrate second surface, said hole being located in said die attachregion of said substrate first surface, said hole in said substratecomprising a length and width parallel to said pressure sensor die firstsurface of approximately 1.0 mm square; attaching said pressure sensordie first surface to said substrate first surface in said die attachregion such that a first region of said pressure sensor die firstsurface covers said hole in said die attach region; applying encapsulantto at least a portion of said substrate first surface and said pressuresensor die second surface, said encapsulant comprising an outer surface;and filling at least a portion of said hole in said substrate withcoupling gel such that said coupling gel covers said first region ofsaid pressure sensor die first surface.
 24. A method for making apressure sensor die package comprising: providing a pressure sensor die,said pressure sensor die comprising a pressure sensor die first surfaceand a pressure sensor die second surface, opposite said pressure sensordie first surface, said pressure sensor die comprising a differentialpressure sensor die with a die hole connecting said second surface ofsaid differential pressure sensor die to a cavity formed in saiddifferential pressure sensor die; providing a substrate, said substratecomprising a substrate first surface and a substrate second surface,opposite said substrate first surface, said substrate first surfacecomprising a die attach region, said substrate further comprising a holeconnecting said substrate first surface and said substrate secondsurface, said hole being located in said die attach region of saidsubstrate first surface, said hole in said substrate comprising a lengthand width parallel to said pressure sensor die first surface ofapproximately 1.0 mm square; attaching said pressure sensor die firstsurface to said substrate first surface in said die attach region suchthat a first region of said pressure sensor die first surface coverssaid hole in said die attach region; applying encapsulant to at least aportion of said substrate first surface and said pressure sensor diesecond surface, said encapsulant comprising an outer surface; filling atleast a portion of said hole in said substrate with coupling gel suchthat said coupling gel covers said first region of said pressure sensordie first surface; forming an encapsulant through hole in saidencapsulant, said encapsulant through hole extending from said outersurface of said encapsulant to a first region of said second surface ofsaid pressure sensor die; and at least partially aligning said die holewith said encapsulant through hole.
 25. A method for making pressuresensor die packages comprising: providing a plurality of pressure sensordice, said pressure sensor dice each comprising a pressure sensor diefirst surface and a pressure sensor die second surface, opposite saidpressure sensor die first surface; forming an array substrate, saidarray substrate comprising an array substrate first surface and an arraysubstrate second surface, opposite said array substrate first surface,said array substrate first surface comprising a plurality of die attachregions, said array substrate comprising a plurality of holes connectingsaid array substrate first surface and said array substrate secondsurface, wherein; each die attach region of said plurality of die attachregions has a corresponding one of said plurality of holes therein;attaching each of said pressure sensor die first surfaces to said arraysubstrate first surface in a corresponding one of said die attachregions such that a first region of each of said pressure sensor diefirst surfaces covers said corresponding hole in each of said die attachregions; applying encapsulant to at least a portion of said arraysubstrate first surface and said pressure sensor die second surfaces,said encapsulant comprising an outer surface; and filling at least aportion of each of said plurality of holes in said array substrate withcoupling gel such that each of said first regions of said first surfacesof said plurality of pressure sensor dice is covered by said couplinggel.
 26. A method for making pressure sensor die packages comprising:providing a plurality of pressure sensor dice, said pressure sensor diceeach comprising a pressure sensor die first surface and a pressuresensor die second surface, opposite said pressure sensor die firstsurface, each of said plurality of pressure sensor dice comprising adifferential pressure sensor die, said plurality of pressure sensor diceeach comprising a die hole connecting said second surface of each ofsaid pressure sensor dice to a cavity formed in each of said pressuresensor dice; forming an array substrate, said array substrate comprisingan array substrate first surface and an array substrate second surface,opposite said array substrate first surface, said array substrate firstsurface comprising a plurality of die attach regions, said arraysubstrate comprising a plurality of holes connecting said arraysubstrate first surface and said array substrate second surface,wherein; each die attach region of said plurality of die attach regionshas a corresponding one of said plurality of holes therein; attachingeach of said pressure sensor die first surfaces to said array substratefirst surface in a corresponding one of said die attach regions suchthat a first region of each of said pressure sensor die first surfacescovers said corresponding hole in each of said die attach regions;applying encapsulant to at least a portion of said array substrate firstsurface and said pressure sensor die second surfaces, said encapsulantcomprising an outer surface; filling at least a portion of each of saidplurality of holes in said array substrate with coupling gel such thateach of said first regions of said first surfaces of said plurality ofpressure sensor dice is covered by said coupling gel; forming aplurality of encapsulant through holes in said encapsulant, eachencapsulant through hole of said plurality of encapsulant through holesextending from said encapsulant outer surface to a first region of saidfirst surface of each of said plurality of pressure sensor dice; and atleast partially aligning each of said die holes with one of saidplurality of array substrate through holes.